Friday August 14,
ECHELON is operated jointly by five spy organizations under
the umbrella of the 1948 UKUSA (pronounced you-koo-za)
signals intelligence (SIGNET) agreement.

The five SIGNET agencies are the NSA in America, Canada's
Communications Security Establishment (CSE), the UK's
Government Communications Headquarters (GCHQ), Australia's
Defense Signals Directorate (DSD) and New Zealand's
Government Communications Security Bureau (GCSB). The NSA is
the senior member and calls virtually all the shots.

The following reports (some of which were mentioned by Vest)
are credible resources for information on ECHELON.